If it was up to me ranged ROA would be equal to melee attack speed, for all classes and before applying any feats. The Rapid shot feat would allow for a player to make an extra attack during a sequence, thus raising the ROA by 1 shot for each sequence and applying a -2 attack penalty while it was active (rapid shot would have to be a toggle feat). Manyshot would be a toggle feat that allowed the ranger to make an attack that fires the correct number of arrows per BAB on each shot while applying the corresponding penalty to those shots, the kicker would be that it slows your ROA to 1 attack per sequence. Also composite bows should have the feat bow strength applied to them so that any user can apply their str to the damage portion of the attack. Bow Str should be left as a ranger feat to reflect the pnp theme of the ranged ranger.
Lets say for ease of number crunching that a player at BAB can get off 100 attacks in a minute through melee. This comes to 20 attack sequences of 5 attacks each. A player using ranged combat and no additional feats would also get 100 attacks over a minute. Using rapid shot that ranged combat used would see 120 attacks in the same minute but at a penalty of -2. If you didnt take SOTR and moved around during that time, like many ranged combat users do, the penalty would be -6 for each shot. A player that uses manyshot full time during that sequence would see 80 attacks during that minute all at -8 to hit. If they also applied rapid shot you would see 100 attacks at -10 to hit. If you also happened to move and didnt have SOTR the total penalty would be -14 to hit.
Setting the world as such adds balance because a ranged combat user would be more likely to pick up SOTR to eliminate the penalties associated with infinate kiteing or might have to make a choice about when to use particular feats. In pnp manyshot is great for taking out large, high hp, but low ac creatures. The penalties may have to be adjusted based on the relative values of AC in the game as we don't see many mobs with low AC and high hp, they tend to be high on both.
A light crossbow user with no feats would see 20 attacks in a minute and a heavy crossbow user would get 10 attacks in the same minute. A repeater user would see 10 attacks of 5 bolts each for 50 attacks in a minute.
Add in rapid reload and the light crossbow user can obtain 100 attacks in a minute as the reload is changed to a free action rather then a move action. A heavy crossbow user would be increased to 20 attacks as the reload is no longer a full round action but a move action. The repeater user would then see 20 attacks of 5 bolts each for 100 attacks in a minute.
So in the end the crossbow does see a slowdown in ROA but it comes up to full martial weapon ROA with the addition of a single feat. Not bad overall for a ranged weapon that can be used by all classes and has a better crit range then a bow. The SRD doesnt list the differences between the light and heavy repeaters in terms of reload times and number of bolts that they can hold so I just listed a blank repeater. The benafit of the repeater is a quick burst of attacks from a weapon with a higher crit range then a bow, which is a game were on critical effect matter a large amount is decent for an exotic feat.
I dont know how rapid shot and crossbows interact in pnp. I would think that so long as you could make multiple attacks in a round you would be able to apply the effects of rapid shot. So a light crossbow user with rapid reload and rapid shot could have 120 attacks in a minute with a total penalty of -2 to each shot. It doesn't seem that rapid shot would work with heavy crossbows or repeaters because you can only reduce the reload time to a move action and thus wouldn't get an additional attack. This is because you can only take 1 standard action with a move action in a single round.